This invention relates to an off-line programming method for robots. More particularly, it relates to a process for adapting to individual robots their work point positions which are stated in work programs arranged without using the robots installed in an actual production line so as to provide instructions for robots to make them perform specified activities.
To make a plurality of robots installed in a production line perform a given work sequence work process, teaching has heretofore been adopted. The work process teaching is conducted in such a manner that, while a production line is stopped, the operator actually operates the robot in accordance with a working order sequence, which is then compiled into a work program. Off-line programming, in place of such work process teaching, is being increasingly introduced in order to reduce the work process teaching load and shorten the downtime of the production line. By off-line programming is meant that work programs, which robots are made to execute, are arranged without actually operating the robots.
FIGS. 7A and 7B are diagrams illustrating a method for arranging a work program through such off-line programming. FIG. 7A shows the off-line method for producing a work program and FIG. 7B shows the method for preparing a work program based on a provisional work program. In FIGS. 7A and 7B, there is shown an arrangement of a production robot 1, a workpiece 2, a programming device 3 provided with robot language editing and robot operation simulating functions, and, in FIG. 7B there is shown another teaching robot 4 installed outside a production line.
It has been so arranged that the off-line work program of FIG. 7A is prepared by the programming device 3 from data it receives on the three-dimensional geometries of the robot 1 and the workpiece 2. In this case, the work point positions of the robot 1 are stated in the work program produced through off-line programming, the positions thereof being set in conformity with a descriptive predetermined coordinate system. The work point positions must consequently be converted into work point positions corresponding to the coordinate system with the robot 1 as a reference unit. The conversion of the work point positions is carried out by inputting numerical values based on the relationship of the robot 1 in a measured work cell to the workpiece 2 in terms of their arrangement or the relationship of the robot 1 in the work cell stated in a drawing and the like to the workpiece 2 in the same terms.
The work program according to the provisional work program of FIG. 7B is prepared in such a manner that work process teaching is performed in order to prepare the provisional work program by using the teaching robot 4. The provisional work program is converted by the programming device 3 into the work program adaptable to the production robot 1. Since the work point positions are set in conformity with a coordinate system of the teaching robot 4 installed outside the production line as a reference unit, they must be converted into the work point positions corresponding to the coordinate system with the production robot 1 as a reference unit. The conversion of the work point positions is carried out by teaching several representative work points at which each robot 1 within the production line works on the same workpiece 2 to obtain coordinate conversion relationships and converting the work point positions stated in the provisional program into those corresponding to the coordinate system with each robot 1 within the production line as a reference unit in terms of coordinates.
However, the actual robot 1 may make errors which cannot be accepted as negligible, including errors in the mechanism of the robot 1, errors inherent in each robot 1 because of deviation from the origin of coordinates with the robot 1 as a reference unit, and local errors arising depending on the working posture of the robot 1 when the front ends of the arms thereof are loaded with a heavy object. Those errors cannot be dealt with by means of mechanical coordinate conversion however accurately the actual measurement or work process teaching is performed.
For the above reasons, the portions where conversion accuracy have not yet been attained must be subjected to work process teaching again even though the work point positions stated in the work program are converted into those corresponding to the coordinate system with each robot 1 as a reference unit. In consequence, the problem is that it is still impossible to reduce a work process teaching load and shorten downtime in the production line.